ATP-induced KaiC hexamerization is necessary for the clock function of KaiC.

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This paper examines the Japanese economy in the 1990s, a decade of economic stagnation. We find that the problem is not a breakdown of the financial system, as corporations large and small were able to find financing for investments. There is no evidence of profitable investment opportunities not being exploited due to lack of access to capital markets. The problem then and still today, is a low productivity growth rate. Growth theory, treating TFP as exogenous, accounts well for the Japanese lost decade of growth. We think that research effort should be focused on what policy change will allow productivity to again grow rapidly. Journal of Economic Literature Classification Numbers: E2, E13, O4, O5,

KaiA, KaiB and KaiC constitute the circadian clock machinery in cyanobacteria, and KaiA activates kaiBC expression whereas KaiC represses it. Here we show that KaiA is composed of three functional domains, the N-terminal amplitude-amplifier domain, the central period-adjuster domain and the C-terminal clock-oscillator domain. The C-terminal domain is responsible for dimer formation, binding to KaiC, enhancing KaiC phosphorylation and generating the circadian oscillations. The X-ray crystal structure at a resolution of 1.8 A of the C-terminal clock-oscillator domain of KaiA from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 shows that residue His270, located at the center of a KaiA dimer concavity, is essential to KaiA function. KaiA binding to KaiC probably occurs via the concave surface. On the basis of the structure, we predict the structural roles of the residues that affect circadian oscillations.

KaiB is a component of the circadian clock molecular machinery in cyanobacteria, which are the simplest organisms that exhibit circadian rhythms. Here we report the x-ray crystal structure of KaiB from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1. The KaiB crystal diffracts at a resolution of 2.6 Å and includes four subunits organized as a dimer of dimers, each composed of two non-equivalent subunits. The overall shape of the tetramer is an elongated hexagonal plate, with a single positively charged cleft flanked by two negatively charged ridges whose surfaces includes several terminal chains. Site-directed mutagenesis of Synechococcus KaiB confirmed that alanine substitution of residues Lys-11 or Lys-43 in the cleft, or deletion of C-terminal residues 95-108, which forms part of the ridges, strongly weakens in vivo circadian rhythms. Characteristics of KaiB deduced from the x-ray crystal structure were also confirmed by physicochemical measurements of KaiB in solution. These data suggest that the positively charged cleft and flanking negatively charged ridges in KaiB are essential for the biological function of KaiB in the circadian molecular machinery in cyanobacteria.

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Detergent-resistant membrane microdomains in the plasma membrane, known as lipid rafts, have been implicated in various cellular processes. We report here that a low-density Triton X-100-insoluble membrane (detergent-resistant membrane; DRM) fraction is present in bovine rod photoreceptor outer segments (ROS). In dark-adapted ROS, transducin and most of cGMPphosphodiesterase (PDE) were detergent-soluble. When ROS membranes were exposed to light, however, a large portion of transducin localized in the DRM fraction. Furthermore, on addition of guanosine 5-3-O-(thio)triphosphate (GTP␥S) to light-bleached ROS, transducin became detergent-soluble again. PDE was not recruited to the DRM fraction after light stimulus alone, but simultaneous stimulation by light and GTP␥S induced a massive translocation of all PDE subunits to the DRM. A cholesterol-removing reagent, methyl-␤-cyclodextrin, selectively but partially solubilized PDE from the DRM, suggesting that cholesterol contributes, at least in part, to the association of PDE with the DRM. By contrast, transducin was not extracted by the depletion of cholesterol. These data suggest that transducin and PDE are likely to perform their functions in phototransduction by changing their localization between two distinct lipid phases, rafts and surrounding fluid membrane, on disc membranes in an activation-dependent manner.The phototransduction system in the photoreceptor rod outer segments (ROS) 1 of vertebrates is a typical G protein-mediated signaling system. In the prevailing model of phototransduction (1), light-excited rhodopsin interacts with the GDP form of the heterotrimeric G protein transducin and stimulates GDP-GTP exchange on its ␣-subunit (T ␣ ). GTP-T ␣ separates from its counterpart, the ␤␥ subunit of transducin (T ␤␥ ), and binds the inhibitory subunit (P ␥ ) of cGMP-phosphodiesterase (PDE), thus releasing the constraint of P ␥ on the catalytic subunits (P ␣ and P ␤ ) of PDE. The resulting decrease in cytoplasmic cGMP leads to the closure of cGMP-gated channels and the hyperpolarization of photoreceptor plasma membranes. Although the signaling cascade of ROS has been intensively studied during the past two decades, the whole mechanism has not yet been elucidated (for review see Ref.2).

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